Nickel(II) bis(acetylacetonate) is a

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

with the formula i(acac)₂sub>3, where acac is the

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

C₅H₇O₂⁻ derived from

deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...

acetylacetone Acetylacetone is an organic compound with the chemical formula . It is a colorless liquid, classified as a 1,3-diketone. It exists in equilibrium with a tautomer . These tautomers interconvert so rapidly under most conditions that they are tre ...

. It is a dark green paramagnetic solid that is soluble in organic solvents such as

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...

. It reacts with water to give the blue-green diaquo complex Ni(acac)₂(H₂O)₂.

Structure and properties

Anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

nickel(II) acetylacetonate exists as molecules of Ni₃(acac)₆. The three nickel atoms are approximately collinear and each pair of them is

bridged Bridging may refer to: Construction * Building of bridges across a gap * Cross bracing used between joists to stabilize them Electronics and computing * In electronics, using a low source impedance to drive a large load impedance for maximum vol ...

by two μ₂ oxygen atoms. Each nickel atom has tetragonally distorted octahedral geometry, caused by the difference in the length of the Ni-O bonds between the bridging and non-bridging oxygens. Ni₃(acac)₆ molecules are almost

centrosymmetric In crystallography, a centrosymmetric point group contains an inversion center as one of its symmetry elements. In such a point group, for every point (x, y, z) in the unit cell there is an indistinguishable point (-x, -y, -z). Such point groups ...

, despite the non-centrosymmetric

point group In geometry, a point group is a mathematical group of symmetry operations (isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every p ...

of the ''cis''-Ni(acac)₂ "monomers," which is uncommon. The trimeric structure allows all nickel centers to achieve an octahedral coordination. The trimer is only formed if intramolecular sharing of oxygen centers between pairs of nickel centers occurs. The anhydrous complex has interesting

magnetic properties Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...

. Down to about 80 K it exhibits normal

paramagnetism Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

with an effective

magnetic moment In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnets ...

of 3.2 μ_B, close to the spin-only moment expected of a d⁸ ion with two unpaired electrons. The effective moment rises to 4.1 μ_B at 4.3 K, due to ferromagnetic exchange interactions involving all three nickel ions. When bound to bulkier analogues of acetylacetonate ligand, steric hindrance favors formation of the mononickel derivatives. This behavior is observed for the derivative of 3-methylacetylacetonate.

Dihydrate

As in the anhydrous form, the Ni(II) centres occupy octahedral coordination sites. The coordination sphere is provided by two bidentate acetylacetonate (acac) ligands and two aquo ligands. Ni(acac)₂(H₂O)₂ exists as cis and trans

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

. Trans isomers are also observed for Ni(acac)₂( pyridine-N-oxide)₂. In the trans isomers, the axial Ni-O bonds are greater in length (2.1000Å) than the equatorial Ni-O bonds (2.0085 Å and 1.9961Å). Ni(acac)2

Synthesis

Bis(2,4-pentanedionato)nickel(II) is prepared by treating

nickel nitrate Nickel nitrate is the inorganic compound Ni(NO3)2 or any hydrate thereof. The anhydrous form is not commonly encountered, thus "nickel nitrate" usually refers to nickel(II) nitrate hexahydrate. The formula for this species is written in two ways ...

with

in the presence of base. The product is the blue-green diaquo complex Ni(CH₃COCHCOCH₃)₂(H₂O)₂. :Ni(NO₃)₂ + 2 CH₃COCH₂COCH₃ + 2 H₂O + 2 NaOH → Ni(CH₃COCHCOCH₃)₂(H₂O)₂ + 2 NaNO₃ This complex can be dehydrated using a Dean–Stark trap by

azeotropic distillation In chemistry, azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. In chemical engineering, ''azeotropic distillation'' usually refers to the specific technique of adding another component to genera ...

: :3 Ni(CH₃COCHCOCH₃)₂(H₂O)₂ → i(CH₃COCHCOCH₃)₂sub>3 + 6 H₂O Upon heating Ni(acac)₂(H₂O)₂ at 170–210 °C under reduced pressure (0.2-0.4 mmHg), the anhydrous form

sublimes Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...

and water is removed.

Reactions

The anhydrous complex reacts with a range of

Lewis bases A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

to give monomeric

adducts An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all co ...

. Illustrative is the reaction with tetramethylethylenediamine (tmeda): : i(CH₃COCHCOCH₃)₂sub>3 + 3 tmeda → 3 Ni(CH₃COCHCOCH₃)₂(tmeda) Ni(acac)₂(H₂O)₂ reacts quickly in high yield at a methine positions, producing diamides from isocyanates. Related reactions occur with

diethyl azodicarboxylate Diethyl azodicarboxylate, conventionally abbreviated as DEAD and sometimes as DEADCAT, is an organic compound with the structural formula CH3CH2O2CN=NCO2CH2CH3. Its molecular structure consists of a central azo functional group, RN=NR, flanked ...

and

dimethyl acetylenedicarboxylate Dimethyl acetylenedicarboxylate (DMAD) is an organic compound with the formula CH3O2CC2CO2CH3. It is a di-ester in which the ester groups are conjugated with a C-C triple bond. As such, the molecule is highly electrophilic, and is widely employed ...

: :Ni(acac)₂(H₂O)₂ + 2 PhNCO → Ni(O₂C₅Me₂C(O)NHPh)₂ + 2 H₂O

Applications

The anhydrous complex is the precursor to nickel-based catalysts such as nickel bis(cyclooctadiene) and

tetramethylethylenediamine(dimethyl)nickel(II) Tetramethylethylenediamine(dimethyl)nickel(II) is the organonickel complex with the formula (Me = CH3). This yellow-brown, air-sensitive compound is popular precursor to diverse organonickel complexes. It is prepared from the tmeda adduct of ...

. i(acac)₂sub>3 is a

precursor Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of unr ...

for the deposition of a

thin film A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...

NiO are two wrathful and muscular guardians of the Gautama Buddha, Buddha standing today at the entrance of many Buddhist temples in East Asian Buddhism in the form of frightening wrestler-like statues. They are dharmapala manifestations of the bo ...

on conductive glass substrates using sol-gel techniques.

References